A hydraulic mount for a vehicle comprises a tubular housing having a mounting bracket at one end, a piston disposed in the housing, and a rod connected to the piston and extending through a seal at the other end of the housing. The piston divides the housing into a piston chamber and a rod chamber. The rod includes a second mounting bracket at the end outside the housing. Hydraulic fluid is pumped into and out of the chambers to move the piston relative to the housing and thereby adjust the distance between the mounting brackets. The hydraulic actuator is installed by attaching the mounting brackets to the stabilizer bar of the wheel assembly and the body, which represents the sprung mass. During use, in response to sensors that detect vehicle roll, the system adjusts the hydraulic fluid in the piston chamber and the rod chamber to length or shorten the actuator and maintain a stable orientation for the vehicle.
Primary fluid flow in an actuator is through external connections to a pump. This is in marked contrast to a damper, also referred to as a shock absorber, wherein the hydraulic fluid is sealed within the housing and fluid flows through internal passages in response to road input. It is known to provide a passage in the piston of the hydraulic actuator to allow limited flow between the piston chamber and the rod chamber. The passage is normally open, and includes a disc valve assembly to close the passage to prevent excessive flow that would interfere with the desired operation of the actuator as determined by the pumped fluid. FIG. 1 shows a conventional disc valve assembly for this purpose. Piston 10 comprises a passage 12 having an enlarged outlet 14 that allow fluid flow in the direction of arrow 15 from the piston chamber to the rod chamber. The assembly includes a disc pack 16 that includes one or more flexible discs, for example discs 18 and 20 in FIG. 1. The assembly includes a spacer 24 between the disc pack and the piston to provide a gap between the free end 22 and the piston 10, so that the valve is normally open to provide communication between the fluid in the chambers with limited flow. In response to excessive fluid pressure in the rod chamber, valve discs 18 and 20 flex toward the piston in the direction of arrow 26, whereupon disc 20 engages the piston to close the valve. In response to excessive pressure in the piston chamber, it is desired to further open the valve to facilitate fluid flow. This is accomplished by flexing valve discs away from the piston, in the direction of arrow 28. A washer 30 limits the flexing to prevent the discs from permanent deformation. A spacer 32 provides clearance to the discs to flex. Circumstances may arise where the fluid pressure to open the valve may create stresses that exceed the yield strength of the disc material and deform the disc. Moreover, repeated flexure may exceed the fatigue limit of the disc material. As a result, the valve may fail to close, interfering with the proper operation of the hydraulic actuator.
Therefore, a need exists for a hydraulic actuator having an improved disc valve assembly that reduces stresses within the valve discs during flexure, and thereby extends the useful life of the actuator.